[Rivet] Born and dressed level in Rivet

[Andy Buckley]

On 03/10/13 17:00, Ulla Blumenschein wrote:
> Dear Andy,
> 
> I  would be very happy if that works out.
> I cc to Oleg  and Tim, who did a comparison of various dressing
> definitions recently.
> Maybe Oleg would be interested to reproduce his plots with the
> proposed new Rivet implementation, to check what the residual effect
> is of the missing " from W/Z" requirement.

I can certainly tell you how to hack an existing Rivet version to do
that. It's a bit low-level, though, so not obvious to me how it would be
done inside a particular analysis. But contact me/us and we'll do what
we can to help.

> I have a technical question: Would only photons dircetly from
> quarkonia decays be excluded?  Where would photons from leptons from
> semileptonic HF decays end up?

Our fromDecay(Particle&) function walks back up the decay chain looking
for a parent hadron or tau with status=2, meaning "physical hadron/tau
which has already been decayed". (Note the double specification: PYTHIA6
predates the standard status codes so we overspecify!) So photons from
charmonia and from hadron decay leptons would count as being from
decays: I assume that is what you want? Special case treatments for
these would take more coding, but if it'll be needed then we should know
now: at the very least this would indicate that the steering flag needs
to have more states than a bool would allow!

Of course this would mean that the ClusteredPhotons projection would
need to be configured differently for charmonia analyses than for W/Z
ones, but that is hardly surprising. And we can leave the flag as
"include all" by default on ClusteredPhotons, but turn it to "non-decay
only" by default for the W/ZFinders. Sound good?

Andy



> On Thu, Oct 3, 2013 at 3:16 PM, Andy Buckley <andy.buckley at cern.ch> wrote:
>> Hi Ulla, all,
>>
>> I've discussed this a bit with Daniel Froidevaux and think that it would
>> make sense for us to at least add a flag to the ClusteredPhotons tool in
>> Rivet to exclude photons which come from hadron decays. Taus are a bit
>> of a borderline case, but that does not affect (current) EW measurements.
>>
>> This is not *exactly* the same definition, but I think that "only
>> photons from W/Z" is hard to implement in a generator-unspecific way.
>>
>> Maybe Frank Siegert wants to comment more on this proposal to use the
>> fromDecay() function in ClusteredPhotons, since he did most of the
>> detailed work to put these W/ZFinders and related classes together.
>>
>> Re. the Born comparisons, I believe that the ATLAS W/Z analyses written
>> so far *don't* compare to the Born-level results, since there *isn't* a
>> generator-portable way to write them. I remember removing a
>> generator-specific code along those lines in a previously submitted
>> analysis for that reason: it's fine for ATLAS-internal versions of
>> analyses but won't go into the public Rivet library.
>>
>> Hope that helps,
>> Andy
>>
>> PS. For those who care, if we agree that that is a reasonable route, I
>> propose that the exclude-decay-photons functionality would go into Rivet
>> 2.0.1 or 2.0.2. The exact version depends on the extent to which we want
>> to separate different types of change -- 2.0.1 might just be adding some
>> "queued" analysis codes, or it could be a combination of that and some
>> definition changes. The numbering does not really reflect anything about
>> the timescales! But note that we'll only be making this change in the
>> Rivet 2 series -- 1.x is in "maintenance mode".
>>
>>
>> On 03/10/13 14:51, Roman Lysak wrote:
>>>
>>>  Hi Ulla,
>>>
>>> I think the Rivet authors are better to replay to your questions so I'm
>>> cc-ing this to them.
>>> Could anyone address Ulla's questions?
>>>
>>> Cheers,
>>>   Roman
>>>
>>> On 10/03/2013 12:25 PM, Ulla Blumenschein wrote:
>>>> Hi Roman,
>>>>
>>>> we have currently a discussion in SM about how to synchronize  the
>>>> Atlas internal definition of dressed leptons with the Rivet
>>>> implementation.
>>>> Currently in SM, we sum all photons emitted from the W/Z decay
>>>> products whereas Rivet sums all photons.
>>>> With the extreme phase spaces which we access with 8TeV there are
>>>> differences up to percentage level between these definitions due to
>>>> pi0 decays from hadronic activity close to leptons.
>>>>
>>>> Is it possible to  implemet an alternate Z finder which can
>>>> discriminate photon sources? I understand that this might be against
>>>> the philosophy of Rivet (MC independence). Or are there other
>>>> problems?
>>>>
>>>> Also the born level Z finder is not completely clear to me. I assumed
>>>> so far that the born level is defined by different status codes in
>>>> different MC generator, so how does Rivet handle this issue?
>>>>
>>>>
>>>> Many thanks in advance,
>>>> Ulla
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Sun, Sep 15, 2013 at 7:46 PM, Roman Lysak <lysak at fzu.cz> wrote:
>>>>>   Hi Ulla,
>>>>>
>>>>>
>>>>>
>>>>> On 09/12/2013 06:51 PM, Ulla Blumenschein wrote:
>>>>>> Hi Roman,
>>>>>>
>>>>>> Could you explain how we define Born and dressed in a generator
>>>>>> independent way in Rivet?
>>>>>
>>>>> it depends on the object type.
>>>>> For example, for Z boson (similarly for W boson), you can specify
>>>>> whether to
>>>>> add photons (next to last one parameter in the constructor below) in
>>>>> a given
>>>>> radius (2nd next to last one parameter) around the leptons from Z
>>>>> decay to
>>>>> the Z boson 4-momentum.
>>>>>
>>>>>        //fiducial phase space + born level
>>>>>        ZFinder zfinder_mu(-2.4, 2.4, 20, MUON, 66.0*GeV, 116.0*GeV, 0.1,
>>>>> false, false);
>>>>>        addProjection(zfinder_mu, "ZFinder_mu");
>>>>>
>>>>>        //for combined cross-sections (combined phase space + dressed
>>>>> level)
>>>>>        ZFinder zfinder_comb_mu(-2.5, 2.5, 20, MUON, 66.0*GeV,
>>>>> 116.0*GeV, 0.1,
>>>>> true, false);
>>>>>
>>>>>
>>>>> Sorry for late response.
>>>>>
>>>>> Cheers,
>>>>>    Roman
>>>>>
>>>>>
>>>>>
>>>>>> Cheers, Ulla
>>>>>>
>>>>>> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>>>>>>       Ulla Blumenschein
>>>>>>       II Physik, Uni Goettingen
>>>>>>       Friedrich-Hund-Platz 1, D01.110
>>>>>>       phone: 0049-551-397645
>>>>>> /_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>>>>>
>>>>
>>>>
>>>
>>> _______________________________________________
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>>
>>
>> --
>> Dr Andy Buckley, Royal Society University Research Fellow
>> Particle Physics Expt Group, University of Glasgow / PH Dept, CERN
> 
> 
> 


-- 
Dr Andy Buckley, Royal Society University Research Fellow
Particle Physics Expt Group, University of Glasgow / PH Dept, CERN